The results also underscore the importance of sleep for this age group.

"It really adds to the growing body of literature that emphasizes the need for children and teens to get sufficient amounts of sleep every night as one of the key ways to promote health and prevent weight gain," study researcher Dr. Susan Redline, a professor of medicine in the Division of Sleep Medicine at Brigham and Women's Hospital and Beth Israel Deaconess Medical Center in Boston, Mass., told LiveScience.

However, the researchers note that their study only shows an association and cannot say for certain whether sleep loss did in fact cause the teens to eat more fatty foods.

Less sleep, more fat
Getting too little sleep has been linked with obesity for both adults and children. Other studies have shown sleep deprivation may alter levels of the hormones that regulate appetite. However, few studies have attempted to bridge the gap to see whether lack of sleep in a non-laboratory setting leads to a change in eating patterns.

Redline and her colleagues examined the sleeping and eating habits of 240 teens ages 16 to 19. For five to seven nights, the teens wore a wrist device that measured their sleeping patterns at home. The device, known as a wrist actigraph, detects movement and can detect whether a person is awake or asleep.

The participants were also interviewed about eating habits over a 24-hour period, giving details about what, when and how much was consumed.

Adolescents who slept fewer than eight hours a night consumed 2.2percent more calories from fat and 3-percent fewer calories from carbohydrates compared with adolescents who slept eight hours or more. The results held even after the researchers took into account factors that might have influenced the association, including gender, age and race, and body mass index, or BMI, a measure of body fat.

"The relative increase in fat consumption among shorter sleepers by 2.2 percent per day chronically may contribute to cumulative increases in energy consumption that would be expected to increase risk for obesity and cardiovascular disease," Redline said.

When the researchers performed what is called a secondary analysis and looked at the data for each gender separately, they found the results were most significant for girls. However, Redline said these results need to be interpreted with caution since breaking up the data in this way might lead to a false result.

Nonetheless, the finding was somewhat surprising, because previous work has shown the obesity-sleep link to be strongest for boys. The current findings could reflect biological differences between boys and girls in their responses to sleep deprivation, or they could result from factors related to the study design. For instance, it could simply be that girls were better at recalling what they ate than boys, Redline said.

Previous work has shown that sleep deprivation causes a decrease in leptin, a hormone that suppresses appetite, and an increase in ghrelin, a hormone that promotes appetite.

In addition, being awake for longer hours means more opportunities to eat. In fact, the researchers found children who got fewer than eight hours of sleep were more likely to eat early in the morning, between 5 a.m. and 7 a.m. It's possible that eating this early, when you're body's internal clock, or circadian rhythm, says you should be asleep, promotes weight gain.